Transient Oscillations In Semiconductor Differential Transmission Spectra

Several semiconductor materials were studied using femtosecond pump-probe spectroscopy. Oscillatory structures are observed in the differential transmission spectra of the probe pulse at the very early times when the probe pulse precedes the pump pulse. These oscillations are around the exciton frequency when pumping is either above or below the exciton, and in the vicinity of the pump frequency when the pump is tuned inside the semiconductor band. The observed data are discussed in terms of semiclassical theory.